Adding and subtracting in columns

Mathematics · Addition & Subtraction · ages 7-8

Name ______________________ Date ____________

Zoe writes 526 + 173 in columns, with 173 under 526. Which digit of 173 should sit under the 6?
- The 3, because they are both ones digits
- The 1, because it is the first digit of 173
- The 7, because it sits in the middle
Checking your answer with the inverse operation means doing the opposite calculation to see if you land back where you started.
Circle one: True False
In the ones column of a subtraction, the top digit is smaller than the bottom digit. What should you do?
- Exchange (borrow) 1 ten from the next column
- Write a zero and move on
- Swap the two digits around and subtract
For 631 - 247 = 384, adding 384 + 247 should return 631.
Circle one: True False
Work out 512 − 278 using columns, exchanging where you need to. What is the answer?
Answer: ______________
Priya added 456 + 237 and got 693. How could she check if this is right?
- Compute 693 - 237 and see if the result is 456
- Add 237 to 693 and see whether the result is 456
- Repeat 456 + 237 exactly and use that as the check
Which estimate is close to 347 + 265?
- About 300
- About 600
- About 900
- About 1,000
Work out 347 + 265 using columns. What is the answer?
Answer: ______________
Tom is adding 347 + 26. He lines up the 6 under the 4 and the 2 under the 3, leaving the ones column of the bottom number empty. How should he line up 26 instead?
- He should add 26 first, then place the answer under 347
- Any lineup is fine if every digit is close to the next one
- Put 6 under 7 in ones, and 2 under 4 in tens
Mia worked out 512 − 278 by saying '2 minus 8, so I'll just do 8 minus 2 and write 6,' without exchanging. What went wrong?
- She should write 0, since 2 take away 8 leaves nothing
- Nothing went wrong, because flipping gives the same answer
- She flipped it; exchange first, then 12 - 8 = 4

Answer key

For grown-ups. Fold this page away before handing over the rest.

Adding and subtracting in columns W1-mt_SrrsLiJkr3-s1

The 3, because they are both ones digits · Columns line up by place value. The 6 in 526 is a ones digit, so the ones digit of 173, which is 3, sits under it.
True · For addition, subtract one of the numbers you added from the total. For subtraction, add the answer back to the number you subtracted.
Exchange (borrow) 1 ten from the next column · Exchanging turns 1 ten from the next column into 10 extra ones, so you can subtract properly.
True · Addition and subtraction undo each other. If 384 is the difference, 384 + 247 should return the starting number 631.
234 · Ones: exchange a ten to make 12 − 8 = 4. Tens: exchange a hundred to make 10 − 7 = 3. Hundreds: 4 − 2 = 2. Answer: 234.
Compute 693 - 237 and see if the result is 456 · Subtracting one of the numbers she added from the total should bring her back to the other number. Adding the total to 237 just makes a new bigger number, and redoing the same addition could repeat the same mistake.
About 600 · Round 347 to 350 and 265 to 270. Their estimated sum is 620, which is close to 600 and far from 300 or 900.
612 · Ones: 7 + 5 = 12, write 2 carry 1. Tens: 4 + 6 + 1 = 11, write 1 carry 1. Hundreds: 3 + 2 + 1 = 6. Answer: 612.
Put 6 under 7 in ones, and 2 under 4 in tens · Line up by place value: ones under ones (6 under 7), tens under tens (2 under 4). The hundreds column then just has the 3 by itself.
She flipped it; exchange first, then 12 - 8 = 4 · In each column you take the bottom digit from the top digit. When the top digit is smaller, exchange a ten first, so 12 - 8 = 4. Flipping to 8 - 2 answers a different question.